Vacuum heat insulator, method of manufacturing the same, and refrigerator using the same

ABSTRACT

A vacuum heat insulator according to the present invention includes a core molded to be plate-shaped with the use of a binding agent. The vacuum heat insulator assumes any one of the following configurations. A) The core is formed by curing a fiber aggregate by means of a binding agent. The fibers have an average fiber diameter of at least 0.1 μm but at most 10 μm, and voids defined by fibers have a void diameter of at most 40 μm. The core has a percentage of the voids of at least 80%. B) The binding agent is varied in concentration in a through-thickness direction of the core. C) A cured layer solidified by the binding agent is formed on at least one side surface of the core. D) The core contains fibers having a length of at most 100 μm. The fibers are oriented perpendicular to a direction of heat transmission. Such vacuum heat insulator is excellent in adiabatic property. Refrigerators, to which such a vacuum heat insulator is applied, are made small in size, or have a large inner volume, or contribute to energy saving.

This application is a U.S. national phase application of PCTinternational application PCT/JP2003/006915.

TECHNICAL FIELD

The present invention relates to a vacuum heat insulator using a coreformed to be plate-shaped, an adiabatic body, an adiabatic box body, anadiabatic door, a storage house, and a refrigerator, to which the vacuumheat insulator is applied, a method of manufacturing the vacuum heatinsulator, and a method of manufacturing the core for the vacuum heatinsulator.

BACKGROUND ART

In recent years, energy saving has been strongly demanded from theviewpoint of prevention of global warming, and energy saving fordomestic electric appliances has become an urgent problem. Inparticular, heat insulators having an excellent adiabatic performance(heat insulating efficiency) are demanded for thermally insulatedequipments such as refrigerators, freezers, automatic vending machines,etc. from the viewpoint of efficient use of heat.

As general heat insulators, fiber materials such as glass wool, etc. andfoam such as urethane foam, etc. are used. In order to enhance theseheat insulators in adiabatic property, it is necessary to increase theheat insulator in thickness. Since there is a limitation to a space,into which heat insulators can be filled, however, such measures cannotbe applied in case of the necessity for space saving and effectivespatial use.

Attention is paid to vacuum heat insulators as heat insulators having ahigh adiabatic performance. Vacuum heat insulators are ones, in which acore is covered by an exterior covering having a gas-barrier quality, aninterior of the exterior covering is reduced in pressure, and an openingof the exterior covering is fused.

Conventional vacuum heat insulators include one, in which an aggregateof inorganic fibers such as glass wool, etc. is cured by a binding agentto be used for a core. Such vacuum heat insulators are described in, forexample, U.S. Patent publication No. 4,726,974 and Japanese PatentUnexamined Publication No. H8-28776. Since an aggregate of inorganicfibers is cured by means of a binding agent, the vacuum heat insulatorhas a sufficient strength and a sufficient planarity to be excellent inhandling quality. However, such a vacuum heat insulator has theadiabatic performance (thermal conductivity) of about 0.007 W/mK at thedegree of vacuum of 1.33 Pa, the adiabatic performance is same as thatof a vacuum heat insulator in which powder filling is used as a core.Thus it is demanded to enhance the adiabatic performance beyond suchadiabatic performance.

DISCLOSURE OF THE INVENTION

A vacuum heat insulator according to the present invention includes acore molded to be plate-shaped with the use of a binding agent. Thevacuum heat insulator assumes any one of the following configurations.

A) The core contains a fiber aggregate. The fibers have an average fiberdiameter of at least 0.1 μm but at most 10 μm, and voids defined byfibers have a void diameter of at most 40 μm. The core has a percentageof the voids of at least 80%.

B) The binding agent is varied in concentration in a through-thicknessdirection of the core.

C) A cured layer solidified by the binding agent is formed on at leastone side surface of the core.

D) The core contains fibers having a length of at most 100 μm. Thefibers are oriented perpendicular to a direction of heat transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a vacuum heat insulator according toa first exemplary embodiment of the present invention.

FIG. 2 is a cross sectional view of a core of a vacuum heat insulatoraccording to a sixth exemplary embodiment of the present invention.

FIG. 3 is a cross sectional view of a core of a vacuum heat insulatoraccording to a seventh exemplary embodiment of the present invention.

FIG. 4 is a cross sectional view of a core of a vacuum heat insulatoraccording to an eighth exemplary embodiment 8 of the present invention.

FIG. 5 is a conceptual view showing an appearance of a surface of thecore, observed with an optical microscope, according to the sixthexemplary embodiment of the present invention.

FIG. 6 is a cross sectional view of a vacuum heat insulator according toa tenth exemplary embodiment of the present invention.

FIG. 7 is a plan view of the vacuum heat insulator according to thetenth exemplary embodiment of the present invention.

FIG. 8 is an exemplary, conceptual view showing an appearance of asurface of a core, observed with an optical microscope, according to athirteenth exemplary embodiment of the present invention.

FIG. 9 is a cross sectional view of a heat insulating element accordingto a fourteenth exemplary embodiment of the present invention.

FIG. 10 is a cross sectional view of a storage shed according to afifteenth exemplary embodiment of the invention.

FIG. 11 is a cross sectional view of a refrigerator according to asixteenth exemplary embodiment of the present invention.

FIG. 12 is an enlarged, cross sectional view of an essential part of aroof surface of a refrigerator-freezer according to an eighteenthexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the drawings. Same constituents are denoted by samereference numerals to be explained, and detailed explanations thereforwill be omitted.

First Exemplary Embodiment

FIG. 1 is a cross sectional view showing a vacuum heat insulatoraccording to a first exemplary embodiment of the present invention.Vacuum heat insulator 1 according to this embodiment includes core 2 andexterior covering 3 covering the same. Exterior covering 3 includes agas-barrier film having a gas-barrier layer and a thermal fusing layer.An interior of exterior covering 3 is reduced in pressure. An opening ofexterior covering 3 is thermally fused. Core 2 is formed by curing aninorganic fiber aggregate, which is laminated by a dry process to havean average fiber diameter of 5 μm, by means of a binding agent to makethe same plate-shaped.

A method of manufacturing vacuum heat insulator 1 will be simplydescribed below. After core 2 is dried at 140° C. for one hour, it isinserted into exterior covering 3. After an interior of exteriorcovering 3 is reduced to 13.3 Pa in pressure, its opening is bonded bythermal fusing.

The adiabatic performance (thermal conductivity) of vacuum heatinsulator 1 fabricated in this manner is measured at an averagetemperature 24° C. to be 0.0035 W/mK. Void diameter between fibers iscalculated by the mercury porosity analysis to present 40 μm. Since core2 cured by a binding agent to be made plate-shaped is used, surfaces ofvacuum heat insulator 1 is sufficiently planar and also sufficient instiffness.

In the mercury porosity analysis, the void diameter (rP) is calculatedby Washburn formula indicated in Formula 1 on the basis of respectivevalues of surface tension (γHg) of mercury, contact angle (θ), andmercury injection pressure (P).rP=2γHg cos θ/P  (Formula 1)

Void diameter corresponding to those respective pressures, under whichmercury is injected, is obtained from an amount of mercury on the basisof Formula 1. Void diameter is determined by calculation from the voiddiameter distribution ranging from 0.1 μm to 40 μm.

Core 2 of vacuum heat insulator 1 according to this embodiment is formedfrom an aggregate of inorganic fibers, Core 2 has a thickness of 15 mm.Core 2 has a void diameter of 40 μm and a percentage of the voids of94%. Core 2 has a decreasing rate of 10% in thickness due to reductionin pressure, and has a density (bulk density) of 150 kg/m³, and pressurein vacuum heat insulator 1 is 13.3 Pa.

Generally, an apparent thermal conductivity (λapp) is the sum of gasthermal conductivity (λg), solid thermal conductivity (λs), radiationthermal conductivity (λr), and convection thermal conductivity (λc), andis represented by Formula 2.λapp=λg+λs+λr+λc  (Formula 2)

However, influences of thermal conduction due to convection can beneglected under reduced pressure of about 20 kPa or less, or in the voiddiameter of the order of 1 mm or less. Thermal conduction due toradiation has no influence under the condition of working temperature of100° C. or lower. Therefore, solid thermal conduction and gas thermalconduction govern thermal conduction in the vacuum heat insulatoraccording to this embodiment.

By decreasing the fiber diameter of that aggregate of inorganic fibers,which constitutes core 2, thermal conduction through fibers decreases.Thermal conduction through contact points of adjacent fibers is alsodecreased and contact resistance is increased. Thereby, solid thermalconduction is decreased.

An increase in percentage of the voids leads to an increase in ratio, atwhich gas thermal conduction occupies all thermal conduction. Bydecreasing the void diameter defined by the aggregate of inorganicfibers, gaseous molecules are limited in movement and a component of gasthermal conduction is decreased, so that gas thermal conduction isdecreased.

Thus, by decreasing the void diameter defined by the aggregate ofinorganic fibers, solid thermal conduction is decreased. By increasingthe percentage of the voids, gas thermal conduction is made dominant.Further, by decreasing the void diameter defined by the aggregate ofinorganic fibers, gas thermal conduction is decreased. Accordingly, avacuum heat insulator having a low thermal conductivity is obtained.Concretely, a sharp improvement in adiabatic performance is achieved byusing an aggregate of inorganic fibers for the core of the vacuum heatinsulator to provide a percentage of the voids of 80% or more and a voiddiameter between fibers of 40 μm or less.

In case of a fine average fiber diameter of less than 0.1 μm, inorganicfibers are decreased in productivity. Such inorganic fibers becometangled in a complex manner to be increased in probability, in whichthey present a fiber arrangement in parallel to a direction of thermalconduction, to be increased in quantity of thermal conduction. When theaverage fiber diameter is fine, complex tangling is liable to generatean aggregate and to lead to an increase in percentage of the voids whilevoids in and between the aggregate are increased. On the other hand, incase of the average fiber diameter over 10 μm, inorganic fibers areincreased in productivity but quantity of thermal conduction throughfibers is increased. Further, because of a decrease in contactresistance, solid thermal conduction is increased. An increase in fiberdiameter leads to an increase in void diameter between fibers. Based onthese matters, by using an aggregate of inorganic fibers having anaverage fiber diameter of at least 0.1 μm but at most 10 μm, a vacuumheat insulator is enhanced in adiabatic performance withoutdeterioration in productivity.

It is preferable to use a core having 80% or more of percentage of thevoids and at most 40 μm of void diameter between fibers. With sucharrangement, the solid thermal conduction is decreased, gas thermalconduction is made dominant, and the gas thermal conduction isdecreased.

By curing an aggregate of inorganic fibers with the use of a binderagent, a vacuum heat insulator being excellent in surface flatness andstiffness is obtained and sharply improved in service condition,productivity, and quality of handling.

Core 2 according to this embodiment is structured such that a decreasingrate of thickness due to reduction in pressure becomes 10% or lower.Therefore, vacuum heat insulator 1 is restricted in dimensional changebefore and after fabrication. That is, vacuum heat insulator 1 issharply improved in dimensional stability.

Moisture adsorbents and gas adsorbents, such as physical adsorbents orchemical adsorbents, may be charged into vacuum heat insulator 1. Withsuch a manner, the vacuum heat insulator is enhanced in reliability. Themechanism of adsorption may be any one of physical adsorption, chemicaladsorption, occulusion, sorption, etc. while substances acting as anon-evaporation type getter are favorable. Concretely, physicaladsorbents include synthetic zeolite, activated carbon, activatedalumina, silica gel, dawsonite, hydrotalcite, etc. It is possible tomake use of, as chemical adsorbents, oxides of alkali metal and alkalineearth metal, hydroxides of alkali metal and alkaline earth metal, etc.In particular, lithium oxide, lithium hydroxide, calcium oxide, calciumhydroxide, magnesium oxide, magnesium hydroxide, barium oxide, andbarium hydroxide act effectively. Calcium sulphate, magnesium sulphate,sodium sulphate, sodium carbonate, potassium carbonate, calciumchloride, lithium carbonate, unsaturated fatty acid, iron compound, etc.also act effectively. Application of a substance, such as barium,magnesium, calcium, strontium, titanium, zirconium, vanadium, etc.,alone, or a getter substance of an alloy of the substances is moreeffective. In order to adsorb and remove at least nitrogen, oxygen,water content, and carbon dioxide, such various getter substances may bemixed together for application.

A fibrous material of core 2 can make use of fiber of an inorganicmaterial, such as glass wool, ceramic fiber, rock wool, glass fiber,alumina fiber, silica-alumina fiber, silica fiber, silicone carbidefiber, etc. having an average fiber diameter of at least 0.1 μm but atmost 10 μm. Taking account of productivity, at least 0.8 μm but at most10 μm is desirable. Although the fiber length is not specificallyspecified, at most 500 mm and further at most 200 mm are desirable.

While a fiber aggregate laminated by the dry process is used for core 2,it is not limited to the dry process. The core is not limited to alaminate. However, when using a laminate, heat transfer betweenrespective layers is hard to occur. Further, it is preferable to use afiber nonwoven web. Thereby, a continuous porous structure is formed inentire core 2, and expansion of an air remaining between layers ofexterior covering 3 and core 2 at the time of reduction in pressure isprevented by the continuous porous structure. Therefore, it is possibleto avoid a situation in which fused edges of exterior covering 3 arebroken, so that quality is made stable.

As exterior covering 3, one capable of cutting off between core 2 and anoutside air is used. For example, a laminate material of metallic foilmade of stainless steel, aluminum, iron, etc. and plastic film is used.Such a laminate material is composed of at least a gas-barrier layer anda thermally fusing layer. A surface protecting layer or the like may beprovided, if required. As the gas-barrier layer, it is possible to usemetallic foil, plastic film on which metal, inorganic oxide,diamond-like carbon, or the like is deposited, or the like. Materialsare not specifically limitative provided that they are used for thepurpose of lessening gas permeation. Metal deposit films are desirablein order to restrict heat leak and to provide an excellent adiabaticperformance. While foil made of aluminum, stainless steel, iron, etc.can be used as the material of metallic foil, it is not specificallylimitative. A material for metal deposition is not specifically limitedto aluminum, cobalt, nickel, zinc, copper, silver, a mixture thereof,etc. As a backing film being subjected to metallic deposition,polyethylene terephthalate, ethylene-vinyl alcohol copolymer resin,polyethylene naphthalate, nylon, polyamide, polyimide, etc. arepreferred. A material for deposition of inorganic oxide is not limitedsilica, alumina, etc. Used as a thermal fusing layer are a low-densitypolyethylene film, a high-density polyethylene film, a non-drawnpolyethylene terephthalate film, a polypropylene film, apolyacrylonitrile film, an ethylene-vinyl alcohol copolymer film, amixture thereof, etc. However, the layer is not limited to these films.It is suitable that the thermal fusing layer have a thickness of 25 to60 μm. This is because it is directed to providing balance amongstability of a sealing quality in a process of pressure reduction andsealing, restriction on entry of gases from end surfaces of thermallyfused portions, and heat leak from surfaces due to thermal conduction incase of a metallic foil as the gas-barrier layer.

Drawn products of a polyethylene terephthalate film or a polypropylenefilm are used for the surface protective layer. In case of providing anylon film outside thereof, flexibility is improved and durabilityagainst folding is improved.

Metallic containers made of iron sheet, stainless sheet, zinc sheet, orthe like may be used for exterior covering 3.

Exterior covering 3 may be bag-shaped like four-side sealed bags, gussetbags, L-shaped bags, pillow bags, center tape sealed bags, or the likeand is not specifically limitative. Metallic sheet may be formed to berectangular-shaped for use.

According to this embodiment, a linear low-density polyethylene film(referred below to as LLDPE) having a thickness of 50 μm is used as thethermal fusing layer. Used as the gas-barrier layer is a film formed bysticking two films, each having evaporated aluminum together atevaporated aluminum surfaces. One of the films is an ethylene-vinylalcohol copolymer film (referred below to as EVOH) having a thickness of15 μm with an evaporated aluminum of a film thickness of 450 angstromthereon. The other of the films is a polyethylene terephthalate film(referred below to as PET) having a thickness of 12 μm with anevaporated aluminum of a film thickness of 450 angstrom thereon. LLDPEof the thermal fusing layer and EVOH of the gas-barrier layer aredry-laminated to constitute one of exterior coverings 3. The other ofexterior coverings 3 uses LLDPE having a thickness of 50 μm as thethermal fusing layer, and an aluminum foil having a thickness of 6 μmthereon as the gas-barrier layer. Nylon having a thickness of 12 μm isused thereon as the protective layer and nylon having a thickness of 12μm is used as the outermost layer.

A method of manufacturing a vacuum heat insulator, according to thisembodiment, includes first fabricating exterior covering 3, thereafterinserting core 2 into exterior covering 3, reducing pressure in thesame, and sealing the same. Alternatively, core 2 and an exteriorcovering composed of a roll-shaped or sheet-shaped laminate film may beplaced in a decompression tank, and vacuum heat insulator 1 may befabricated by thermally fusing the exterior covering after the exteriorcovering is put in a state of being placed along core 2. Vacuum heatinsulator 1 may be manufactured by directly reducing pressure inexterior covering 3 with core 2 inserted thereinto and sealing theopening of exterior covering 3. Vacuum heat insulator 1 may bemanufactured by inserting board-shaped core 2 into a container which isformed from a metallic sheet, connecting a vacuum pump and the metalliccontainer by means of a pipe to reduce pressure in the container, andthereafter sealing and cutting the pipe. In this manner, there arevarious methods but the method is not limitative.

The core may be dried prior to insertion into the exterior covering, andadsorbents may be inserted together with the core when inserted into theexterior covering.

Second Exemplary Embodiment

Vacuum heat insulator 1 according to this embodiment is the same infundamental constitution as that of the first exemplary embodiment shownin FIG. 1. This embodiment is different from the first exemplaryembodiment in the structure of core 2. Core 2 in this embodiment isformed by coating an inorganic fiber aggregate which is laminated by thedry process to have an average fiber diameter of 7 μM, with a solidcomponent of a phenol resin of 10 wt % as a binding agent and curing thesame to make the same plate-shaped.

The adiabatic performance (thermal conductivity) of vacuum heatinsulator 1 fabricated in this manner is measured at an averagetemperature 24° C. to be 0.0041 W/mK. Curing is adequately achievedsince addition of the binding agent is 10 wt %. Since a decreasing rateof the thickness of core 2 due to reduction in pressure becomes 6%,atmospheric compression is small when vacuum heat insulator 1 is made,and the dimensional stability is sharply improved.

Core 2 of vacuum heat insulator 1 according to this embodiment iscomposed of an aggregate of inorganic fibers having a fiber diameter of7 μm and has a thickness of 15 mm. Core 2 has a void diameter of 40 μmand a percentage of the voids of 92%. A decreasing rate of the thicknessof core 2 due to reduction in pressure is 6%, a density (bulk density)of the core is 200 kg/m³, and pressure in vacuum heat insulator 1 is13.3 Pa.

A binding agent in this embodiment includes an organic binder having atleast a thermosetting property. Fatty acid denatured alkyd resins, aminoresins, epoxy resins, polyamide resins, urethane resins, acrylic resins,petroleum resins, urea resins, melamine resins, xylene resins, furanresins, etc. in addition to phenol resins may be used as such organicbinder. An addition of the binding agent is appropriately 8 to 20 wt %relative to a weight of the core and preferably 10 wt %.

Thus this embodiment includes an organic binder having at least athermosetting property in addition to the constitution of the firstexemplary embodiment. Thereby, an aggregate of inorganic fibers prior tocuring of the binding agent can be subjected to compression molding intoan optional shape with the use of a molding die. When heated in a stateof compression molding in the molding die, the binding agent is cured byheating, so that the molded core is made stable in shape.

The remainder of the constitution is the same as that of the firstexemplary embodiment, and so an explanation therefor is omitted.

Third Exemplary Embodiment

Vacuum heat insulator 1 according to a third exemplary embodiment is thesame in fundamental constitution as that of the first exemplaryembodiment shown in FIG. 1. This embodiment is different from the firstexemplary embodiment in the structure of core 2. Core 2 in thisembodiment is formed by coating an inorganic fiber aggregate which islaminated by the dry process to have an average fiber diameter of 0.8μm, with a phenol resin of 10 wt % as a solid component and curing thesame to make the same plate-shaped.

The adiabatic performance (thermal conductivity) of vacuum heatinsulator 1 fabricated in this manner is measured at an averagetemperature 24° C. to be 0.0024 W/mK. Curing is adequately achievedsince addition of the binding agent is 10 wt %. Since a decreasing rateof the thickness of core 2 due to reduction in pressure is 5%,atmospheric compression is small when vacuum heat insulator 1 is made,and the dimensional stability is sharply improved.

Core 2 of vacuum heat insulator 1 according to this embodiment iscomposed of an aggregate of inorganic fibers having a fiber diameter of0.8 μm and has a thickness of 15 mm. Core 2 has a void diameter of 9 μmand a percentage of the voids of 92%. A decreasing rate of the thicknessof core 2 due to reduction in pressure is 5%, a density (bulk density)of the core is 200 kg/m³, and pressure in vacuum heat insulator 1 is13.3 Pa.

In this manner, according to this embodiment, a vacuum heat insulator,which is easy to mold, stable in shape, and excellent in adiabaticproperty, is obtained in the same manner as in the second exemplaryembodiment.

Fourth Exemplary Embodiment

Vacuum heat insulator 1 according to this embodiment is the same infundamental constitution as that of the first exemplary embodiment shownin FIG. 1. This Embodiment is different from the first exemplaryembodiment in the structure of core 2. Core 2 in this embodiment isformed by coating an inorganic fiber aggregate which is laminated by thedry process to have an average fiber diameter of 3.5 μm, with a bindingagent of 10 wt % as a solid component and curing the same to make thesame plate-shaped. The binding agent includes water glass differentlyfrom the first and second embodiments.

The adiabatic performance (thermal conductivity) of vacuum heatinsulator 1 fabricated in this manner is measured at an averagetemperature 24° C. to be 0.0029 W/mK. Curing is adequately achievedsince addition of the binding agent is 10 wt %. Since a decreasing rateof the thickness of core 2 due to reduction in pressure is 10%,atmospheric compression is small when vacuum heat insulator 1 is made,and the dimensional stability is sharply improved.

Core 2 of vacuum heat insulator 1 according to this embodiment iscomposed of an aggregate of inorganic fibers having a fiber diameter of3.5 μm and has a thickness of 15 mm. Core 2 has a void diameter of 30 μmand a percentage of the voids of 90%. A decreasing rate of the thicknessof core 2 due to reduction in pressure is 10%, a density (bulk density)of the core is 250 kg/m³, and pressure in vacuum heat insulator 1 is13.3 Pa.

In this manner, according to this embodiment, a vacuum heat insulatorwhich is easy to mold, stable in shape, and excellent in adiabaticproperty, is obtained in the same manner as in the second embodiment.Since the density (bulk density) of the core is 250 kg/m³, the core isfurther increased in stiffness to lead an increase in mechanicalstrength when vacuum heat insulator 1 is made, so that shape stabilityis improved in use.

The binder in this embodiment includes an inorganic binder having atleast a thermosetting property. Alumina sol, colloidal silica,organo-silica sol, sodium silicate, lithium silicate, potassiumsilicate, silica magnesium oxide, gypsum, boric acid compounds,phosphoric acid compounds, alkyl silicate, etc. in addition to waterglass may be used as such inorganic binder. Boric acid base compoundsinclude respective hydrates of boric acid, metaboric acid, boric oxideand tetra sodium borate, or anhydrates of sodium borate group, ammoniumborate group, lithium borate group, manganese borate group, calciumborate group, aluminum borate group, zinc borate group, perborate group,alkylborate group, boroxine derivatives, etc. Phosphoric acid compoundsinclude phosphoric acid, phosphorus oxides such as diphosphatepentaoxide or the like, or monobasic phosphate, dibasic phosphate,tribasic phosphate, pyrophosphate, tripolyphosphate, metaphosphate,etc., and their sodium salt, potassium salt, ammonium salt, magnesiumsalt, aluminum salt, etc. Among these substances, glass formingsubstances, or water soluble substances are preferable to include, forexample, boric acid, metaboric acid, boric oxide, borax, or phosphoricacid, monobasic aluminum phosphate, sodium hexametaphosphorate, etc. Oneor two or more of the substances described above are mixed, or otherbinding agents are mixed, or they are diluted to be used as a bindingagent for moldings to fabricate a core. An addition of the binding agentis appropriately 0.1 to 20 wt % relative to a weight of the core andpreferably 1 to 10 wt %.

The remainder of the constitution is the same as that of the secondexemplary embodiment, and so an explanation therefor is omitted.

The organic binder described with respect to the second and thirdembodiments and the inorganic binder described above may be combined tobe used a binding agent.

Fifth Exemplary Embodiment

Vacuum heat insulator 1 according to this embodiment is the same infundamental constitution as that of the first exemplary embodiment shownin FIG. 1. This embodiment is the same in fundamental materials as thosein the second exemplary embodiment. This embodiment is different fromthe second embodiment in the density of core 2. That is, according tothis embodiment, an inorganic fiber aggregate which is laminated by thedry process to have an average fiber diameter of 0.8 μm is coated with asolid component of a binding agent of 10 wt % and cured to be madeplate-shaped, and its density (bulk density) is 250 kg/m³.

The adiabatic performance (thermal conductivity) of vacuum heatinsulator 1 fabricated in this manner is measured at an averagetemperature 24° C. to be 0.0023 W/mK. Curing is adequately achievedsince addition of the binding agent is 10 wt %. Further, since adecreasing rate of the thickness of core 2 due to reduction in pressureis 2%, atmospheric compression is small when vacuum heat insulator 1 ismade, and the dimensional stability is sharply improved.

Core 2 of vacuum heat insulator 1 according to this embodiment iscomposed of an aggregate of inorganic fibers having a fiber diameter of0.8 μm and has a thickness of 15 mm. Core 2 has a void diameter of 8 μmand a percentage of the voids of 90%. A decreasing rate of the thicknessof core 2 due to reduction in pressure is 2%, a density (bulk density)of the core is 250 kg/m³, and pressure in vacuum heat insulator 1 is13.3 Pa.

In this manner, according to this embodiment, a vacuum heat insulatorwhich is easy to mold, stable in shape, and excellent in adiabaticproperty, is obtained in the same manner as in the fourth exemplaryembodiment.

Core 2 according to this embodiment appropriately has a density of 100to 400 kg/m³ and preferably 150 to 250 kg/m³. When the density of thecore exceeds 400 kg/m³, shape stability is further improved but solidthermal conduction is increased to lead to a decrease in adiabaticperformance and an increase in weight, which makes handling hard. Whenthe density of the core is less than 100 kg/m³, vacuum heat insulator 1is decreased in strength. This is the same with other embodiments.

A binding agent used in this embodiment may include an inorganic binderin the same manner as in the fourth exemplary embodiment.

An explanation will be given hereinafter to a conventional vacuum heatinsulator which departs from the respective structures described in thefirst to fifth exemplary embodiments.

First, an explanation is given to the case where an inorganic fiberaggregate having an average fiber diameter of 4.5 μm is used as a coreof a vacuum heat insulator and is not cured by a binding agent.Fabrication is performed in the same manner as the first exemplaryembodiment with respect to other matters. A core of the vacuum heatinsulator has a thickness of 15 mm, a void diameter of 35 μm and apercentage of the voids of 93%. A decreasing rate of the thickness ofthe core due to reduction in pressure is 80%, a density (bulk density)of the core is 180 kg/m³, and pressure in the vacuum heat insulator is13.3 Pa.

While the thermal conductivity of the vacuum heat insulator is favorably0.0022 W/mK, surfaces of the vacuum heat insulator become wavy and thevacuum heat insulator is not sufficient in performance with respect tosurface flatness and stiffness because the inorganic fiber aggregate isnot cured by a binding agent. The decreasing rate of the thickness ofthe core due to reduction in pressure is as large as 80%, and the vacuumheat insulator is poor in dimensional stability to be unfit for use.

Subsequently, an explanation is given to the case where an inorganicfiber aggregate having an average fiber diameter of 0.8 μm is used as acore of a vacuum heat insulator and dried and compressed after beingimmersed in water. The inorganic fiber includes ceramic fibers or thelike of which components are not soluble in water. Fabrication isperformed in the same manner as the first exemplary embodiment withrespect to other matters. A core of the vacuum heat insulator has athickness of 15 mm, a void diameter of 10 μm and a percentage of thevoids of 92%. A decreasing rate of the thickness of the core due toreduction in pressure is 40%, a density of the core is 200 kg/m³, andpressure in the vacuum heat insulator is 13.3 Pa.

While the thermal conductivity of the vacuum heat insulator is favorably0.0028 W/mK, surfaces of the vacuum heat insulator become wavy and thevacuum heat insulator is not sufficient in performance with respect tosurface flatness and stiffness because the inorganic fiber aggregate isnot cured by a binding agent. A decreasing rate of the thickness of thecore due to reduction in pressure is as large as 40%, and the vacuumheat insulator is poor in dimensional stability.

Subsequently, an explanation is given to the case where an inorganicfiber aggregate having an average fiber diameter of 0.8 μm is cured by abinding agent to provide a plate-shaped core of a vacuum heat insulatorand a density of the core is 65 kg/m³. Fabrication is performed in thesame manner as the first exemplary embodiment with respect to othermatters. A core of the vacuum heat insulator has a thickness of 15 mm, avoid diameter of 20 μm and a percentage of the voids of 97%. Adecreasing rate of the thickness of the core due to reduction inpressure is 66%, a density of the core is 65 kg/m³, and pressure in thevacuum heat insulator is 13.3 Pa.

While the thermal conductivity of the vacuum heat insulator is favorably0.0041 W/mK, the density of the core is 65 kg/m³, and the core is notsufficient in stiffness. Since the density of the core is 65 kg/m³, thedecreasing rate of the thickness of the core due to reduction inpressure is as large as 66%, and the vacuum heat insulator is poor indimensional stability.

Subsequently, an explanation is given to the case where a core of avacuum heat insulator includes an inorganic fiber aggregate having anaverage fiber diameter of 4.5 μm and a density of the core is 700 kg/m³.Fabrication is performed in the same manner as the first exemplaryembodiment with respect to other matters. The core of the vacuum heatinsulator has a thickness of 15 mm, a void diameter of 35 μm and apercentage of the voids of 72%. A decreasing rate of the thickness ofthe core due to reduction in pressure is 1%, a density of the core is700 kg/m³, and pressure in the vacuum heat insulator is 13.3 Pa.

Since the core has a density of 700 kg/m³, the core of the vacuum heatinsulator is harder than needed. Therefore, the decreasing rate of thethickness of the core due to reduction in pressure becomes 1%, so thatthe vacuum heat insulator is improved in dimensional stability butsharply decreased in workability. While the core is further increased instiffness and the vacuum heat insulator is enhanced in dimensionalstability when being formed, solid thermal conduction is increasedbecause solid point contact is increased. Therefore, as compared with acore containing no binding agent, the adiabatic performance is sharplydecreased and the thermal conductivity is 0.0058 W/mK.

Summarizing the first to fifth exemplary embodiments and theconventional vacuum heat insulators, it is preferred that an inorganicfiber aggregate used for a core of a vacuum heat insulator be formed tobe plate-shaped and cured by a binding agent. It is found that inorganicfibers preferably have an average fiber diameter of at least 0.1 μm butat most 10 μm, voids defined by inorganic fibers have a void diameter ofat most 40 μm and a core have a percentage of the voids of at least 80%.The reason for this has been described with respect to the firstexemplary embodiment and so a detailed explanation is omitted.

It is found that by curing an aggregate of inorganic fibers with the useof a binder agent, a vacuum heat insulator can be made excellent insurface flatness and stiffness and sharply improved in servicecondition, productivity, and quality of handling.

It is found that when a core has a density of at least 100 kg/m³ but atmost 400 kg/m³, the core can be increased in stiffness while maintainedin adiabatic performance, and the vacuum heat insulator is increased inmechanical strength when made and enhanced in shape stability in use.

By structuring a core so that a decreasing rate of the thickness of thecore due to reduction in pressure becomes 10% or less, dimensionalchanges before and after fabrication of a vacuum heat insulator arerestricted, that is, dimensional stability is greatly improved.

At least an organic binder, or at least an inorganic binder ispreferable as a binding agent to fix an inorganic fiber aggregate in amolded form. Further, a binding agent is more preferable to have athermosetting property. By using such binding agent, an inorganic fiberaggregate prior to curing of the binding agent can be readily subjectedto compression molding into an optional shape. When heating is performedin a state of compression molding with a molding die, a core becomesstable in shape since the binding agent is cured.

An inorganic fiber aggregate is described as being used for a core of avacuum heat insulator. However, a material of fibers is not limitedthereto but may be an organic material. Organic fibers including naturalfibers such as cotton, etc. and synthetic fibers such as polyester,nylon, aramid, etc. can be used for the organic fibers.

Sixth Exemplary Embodiment

Across sectional view of a vacuum heat insulator according to a sixthexemplary embodiment of the invention is the same as FIG. 1 in the firstexemplary embodiment, and the sixth exemplary embodiment is the same infundamental constitution except a core as the first exemplaryembodiment. FIG. 2 is a cross sectional view of a core of the vacuumheat insulator according to the sixth exemplary embodiment of thepresent invention.

Molded body 4 is molded by laminating glass wool having an average fiberdiameter of 5 μm, an average fiber length of 10 mm, and a true specificgravity of 2.5 g/cm³ to a predetermined shape. Binding agent 5 isprepared by dissolving water glass of 10 wt % in water of 90 wt %. Thewater solution of water glass having the same weight as that of glasswool is used. The water solution of water glass is sprayed onto bothsurfaces of molded body 4 by means of a spray device, and then ispressed in a hot blast circulating furnace at 450° C. for 20 minutes.Thus core 2 having a thickness of 15 mm and a density of 235 kg/m³ isobtained. Core 2 has a thermal conductivity of 0.35 W/mK.

A central layer of core 2 fabricated in the above manner is small incontent of binding agent 5, and a large quantity of binding agent 5 iscured nearer to a surface layer to form a hardened layer on the surface.The core has a surface hardness of 65. In observing an appearance of thesurface of core 2 with an optical microscope, fibers crossing oneanother are bound and cured by the binding agent as shown in FIG. 5.

Hardness is defined by a value obtained when hardness of a surface of acore is measured by a durometer, and it is meant that the larger thevalue the harder and the smaller the value the softer.

Vacuum heat insulator 1 is fabricated in the following manner. First,core 2 is dried in a drying furnace at 140° C. for one hour. Thereafter,core 2 is inserted into exterior covering 3. An interior of the exteriorcovering is reduced in pressure up to 3 Pa and sealed.

The thermal conductivity of vacuum heat insulator 1 is 0.0022 W/mK at anaverage temperature 24° C. The surface hardness is 70. In evaluatingdeterioration of the heat insulator through an accelerated test in orderto ascertain reliability with passage of time, the thermal conductivityunder conditions of passage of 10 years is 0.0050 W/mK at an averagetemperature 24° C. At this time, core 2 has a surface hardness of 60.

Seventh Exemplary Embodiment

Vacuum heat insulator 1 according to a seventh exemplary embodiment isthe same in fundamental constitution as that of the sixth exemplaryembodiment. This embodiment is different from the sixth exemplaryembodiment in a binding agent for a core and a molding method.

Binding agent 5 used for a core according to this embodiment is preparedby dissolving a boric acid of 3 wt % in water of 97 wt %. The watersolution of boric acid having the same weight as that of glass wool isused.

The water solution of boric acid is sprayed onto both surfaces of amolded body 4 by means of a spray device, and then is once pressed at aroom temperature of around 25° C. Subsequently, it is pressed in a hotblast circulating furnace at 350° C. for 20 minutes, and thus a core 2having a thickness of 15 mm, a density of 200 kg/m³, a thermalconductivity of 0.34 W/mK is obtained. As similar to the sixth exemplaryembodiment, a central layer of core 2 is also bound by a slight quantityof binding agent 5, and the binding agent is increased in quantitytoward a surface layer. That is, the core according to this embodimentis also formed on a surface thereof with a hardened layer. Core 2 has asurface hardness of 45.

Vacuum heat insulator 1 making use of such core 2 has a thermalconductivity of 0.0020 W/mK at an average temperature 24° C., athickness of 14 mm with 1 mm compressed, and a density of 214 kg/m³. Thesurface hardness is 60. After respective dimensions of the core in astate of being in the vacuum heat insulator is measured, the vacuum heatinsulator is disassembled and a weight of the core is measured, fromresults of which a density may be calculated. In evaluatingdeterioration of the heat insulator through an accelerated test in orderto ascertain reliability with passage of time, the thermal conductivityunder conditions of passage of 10 years is 0.012 W/mK at an averagetemperature 24° C. At this time, core 2 has a surface hardness of 35.

As compared with the vacuum heat insulator according to the sixthexemplary embodiment, the binding agent includes a boric acid andpressing at room temperature is performed prior to heating compression,so that the binding agent remains also in the inside of the core and iscured inside the surface layer without generation of migration.Therefore, an interior of the core is enhanced in stiffness and as awhole in strength.

In the above manufacturing method, laminated fibers coated with thebinding agent prior to heating compression are compressed at a lowertemperature than 100° C. Compression at room temperature in whichmoisture is hard to evaporate, is more preferable.

Subsequently, heating compression is performed at temperature of 100° C.or higher, which aims at evaporation of moisture and curing of thebinding agent, so heating at a higher temperature than the curingtemperature of the binding agent is desirable. 600° C. or lower ispreferable from the viewpoint of preventing the binding agent frompermeating into the laminate excessively and fusion of fibers at thetime of heating compression.

Generally, when fibers coated with a binding agent at the time offiberization are used to fabricate a molded body, a plate-shaped bodyhaving a uniform distribution of the binding agent in the molded body iseasily obtained and so it is difficult to obtain a molded body having aconcentration gradient. According to the manufacturing method accordingto this embodiment, however, fibers are laminated in a predeterminedconfiguration and a binding agent is coated on at least one surface ofthe laminated fibers. The laminated fibers are once compressed at alower temperature than 100° C., that is, a temperature lower than orequal to the evaporating temperature of moisture. Thereby, a state comesout, in which a surface layer is large in concentration of the bindingagent and an interior is small in concentration of the binding agent.Subsequently, compressing and heating are performed at a temperature ofat least 100° C. to evaporate the moisture. Thereby, it is possible toobtain a core in which the concentration of the binding agent is variedin a through-thickness direction and a small quantity of binding agentbinds in the molded body, and which is excellent in strength.

Subsequently, an example of analysis of the concentration distributionof a binding agent in a direction along the thickness of core 2 isindicated. FIG. 3 is a cross sectional view showing a core of a vacuumheat insulator according to this embodiment. First, core 2 is dividedinto front and back surface layers of 1 mm in a through-thicknessdirection to provide skin layers 2A, and a remaining inner layer of thecore is divided into three layers, that is, two outer layers toconstitute intermediate layers 2B, and an innermost layer to constitutecentral layer 2C.

Samples having a weight of 1 g are collected from skin layers 2A,intermediate layers 2B, and central layer 2C to be torn to small pieces,and pure water of 100 ml is added to the respective samples of 1 g,shaken lightly, and mixed. The binding agent is eluted by ultrasonicbath for 15 minutes and its effluent is filtered. A quantity of boroneluted in the filtrate is found by ICP emission spectroscopic analysismethod. Table 1 indicates the results. An eluted quantity per eachsample of 1 g is 3190 μg for skin layers 2A, 2050 μg for intermediatelayers 2B, and 995 μg for central layer 2C. The same test was carriedout in order to find a quantity of boron eluted from glass wool 4 withthe result that the eluted quantity was 182 μg. Accordingly, it is foundthat the binding agent is contained in ratios per each layer of 1 g suchthat 28.5% of the total quantity of the binding agent is contained inskin layer 2A, 17.7% is contained in intermediate layer 2B, 7.7% iscontained in central layer 2C, 17.7% is contained in intermediate layer2B on the opposite side, and 28.5% is contained in skin layer 2A on afront side thereof.

TABLE 1 Analytical value Correction value Concentration of quantity ofquantity distribution of boron of boron of boric (μg/g) (μg/g) acid (%)Skin layer 2A 3190 3013 28.5 (upper side) Intermediate layer 2050 187317.7 2B (upper side) Central layer 2C 995 818 7.6 Intermediate layer2050 1873 17.7 2B (lower side) Skin layer 2A 3190 3013 28.5 (lower side)Glass wool 4 182 — —

The values of concentration distribution of the binding agent areexemplary, the values are preferably varied in a through-thicknessdirection, and the surface layers of the core are more preferably largerin concentration of the binding agent than an interior thereof.

For example, it suffices that skin layers 2A be preferably larger inconcentration of the binding agent than central layer 2C, andintermediate layer 2B be preferably larger in concentration of thebinding agent than skin layers 2A, or intermediate layer 2B bepreferably smaller in concentration of the binding agent than centrallayer 2C.

Ratios, in which the core is divided, are not specifically prescribed.

This is applicable to both a core prior to fabrication of a vacuum heatinsulator and a core taken out by disassembling the vacuum heatinsulator after the fabrication.

The above analytical method is exemplary, and provided that distributionof quantities of the binding agent is found, the analytical method isnot specifically prescribed. It is enough to find that the binding agentis varied in concentration when visually seeing a cross section of acore.

Eighth Exemplary Embodiment

Vacuum heat insulator 1 according to an eighth exemplary embodiment isthe same in fundamental constitution as that of the seventh exemplaryembodiment. According to this embodiment, a core includes plate-shapedmolded bodies of multi-layered structure.

FIG. 4 is a cross sectional view of a core of a vacuum heat insulatoraccording to this embodiment. In FIG. 4, core 2 includes threeplate-shaped molded bodies (referred below to as molded bodies) 4A, 4Bhaving substantially the same thickness.

Two molded bodies 4A include glass wool which has an average fiberdiameter of 5 μm, an average fiber length of 10 mm, and a true specificgravity of 2.5 g/cm³, and are formed by laminating to predeterminedshapes, and a binding agent is added to the molded bodies. The bindingagent is prepared by dissolving a boric acid of 5 wt % in water of 95 wt%. The water solution of boric acid having the same weight as that ofglass wool is used. The water solution of boric acid is sprayed ontoboth surfaces of the molded bodies by means of a spray device, and thenis pressed at room temperature. They are pressed in a hot blastcirculating furnace at 350° C. for 20 minutes, and molded bodies 4Ahaving a thickness of 5 mm and a density of 230 kg/m³ are obtained.

Another molded body 4B is formed by subjecting glass wool which has anaverage fiber diameter of 5 μm and an average fiber length of 10 mm, tocompressing and heating at 350° C. without the use of a binding agent,and has a thickness of 5 mm and a density of 220 kg/m³.

Three plate-shaped molded bodies 4A, 4B are used to be overlapped suchthat molded bodies 4A with a boric acid are disposed outside and moldedbody 4B with only glass wool is disposed inside, thus providing core 2.Molded body 4A is disposed on the surface is a cured layer. Its surfacehardness is 45. Entire core 2 has a density of 190 kg/m³ and a thermalconductivity of 0.34 W/mK.

Vacuum heat insulator 1 with such core 2 has a thermal conductivity of0.0019 W/mK at an average temperature 24° C. and a surface hardness of60. In evaluating deterioration of the heat insulator through anaccelerated test in order to ascertain reliability with passage of time,the thermal conductivity under conditions of passage of 10 years is0.014 W/mK at an average temperature 24° C. At this time, core 2 has asurface hardness of 35.

Since the plate-shaped molded bodies with a boric acid binding agent areprovided for the surface layers and the plate-shaped molded body withonly glass wool is provided for the central layer, a core having a smallsolid thermal conductivity and an excellent adiabatic performance isobtained because of absence of a binding agent in the central layer.

Subsequently, an explanation is given to a vacuum heat insulator, inwhich a binding agent is evenly dispersed unlike the sixth to eighthexemplary embodiments.

A comparative example is the same in fundamental constitution as that ofthe sixth exemplary embodiment. A core is prepared by spraying a bindingagent on fiber surfaces of glass wool which has an average fiberdiameter of 5 μm after fiberization, so that the binding agent evenlyadheres the surfaces. The binding agent is prepared by dissolving aphenol resin of 10 wt % in water of 90 wt %. A water solution of phenolresin having the same weight as that of glass wool is used.

The raw stock with the binding agent is laminated to a predetermineddensity, and pressed in a hot blast circulating furnace at 200° C. for20 minutes in a manner to have a density of 200 kg/m³. The corefabricated in this manner is dried in a drying furnace at 140° C. forone hour, and inserted into an exterior covering, and an interior of theexterior covering is reduced in pressure to 3 Pa and sealed.

The vacuum heat insulator of the above comparative example has a thermalconductivity of 0.0040 W/mK at an average temperature 24° C. However, inevaluating deterioration of the heat insulator through an acceleratedtest in order to ascertain reliability, the thermal conductivity underconditions of passage of 10 years is 0.021 W/mK at an averagetemperature 24° C. Since a phenol resin is used for the binding agentand evenly cured in the core, both the initial capacity and the capacitywith passage of time are degraded as compared with the sixth exemplaryembodiment.

Since the binding agent is evenly cured, the initial performance isdegraded and a long period of time for exhaustion at the time offabrication of the vacuum heat insulator is needed as compared with theseventh exemplary embodiment. In molding a core by the use of fiberssuch as glass wool, etc. and a binding agent, the core has a large solidthermal conductivity when the binding agent is dispersed throughout theglass wool to put individual fibers in a bound state over an interior ofthe fiber molded body.

In contrast, portions in which the binding agent is small inconcentration are provided according to the sixth to eighth exemplaryembodiments, whereby the solid thermal conductivity becomes small andthe adiabatic performance is improved. The portions in which the bindingagent is small in concentration are decreased in resistance toexhaustion, so that a period of time required for evacuation isshortened and the vacuum heat insulator is enhanced in productivity. Byusing such a core that the binding agent is varied in concentration in athrough-thickness direction of a molded body, there is obtained a vacuumheat insulator which is excellent in stiffness of a core, adiabaticperformance, and productivity.

With the above structure, the surface layers are preferably larger inconcentration of the binding agent than the inner layer in athrough-thickness direction of the core. That is, it is preferable toform cured layers on the surfaces. With the construction, in addition tothe above effect, it is possible to obtain a core having an excellentsurface flatness and a vacuum heat insulator being excellent in outwardappearance.

In the sixth to eighth exemplary embodiments, core 2 may include a boardmade of organic or inorganic fibers, a board formed by solidification ofpowder, etc. and is not specifically limitative.

For example, a core including a board made of a fibrous material can usea known material such as inorganic fibers, or organic fibers includingnatural fibers such as cotton, etc. and synthetic fibers such aspolyester, nylon, aramid, etc as described in the first exemplaryembodiment.

A core including a board formed by solidification of powder can useinorganic powder such as silica, pearlite, carbon black, etc.Alternatively, known materials are usable as by solidifying organicpowder such as powder of synthetic resins, etc. by means of a fiberbinding agent, or inorganic or organic liquid binding agent.

With the above structure, however, use of a fibrous material for a coreis preferable. Use of a fibrous material makes it possible to obtain avacuum heat insulator which is easy to mold, small in solid thermalconductivity, that is, has excellent in moldability and adiabaticproperty. In particular, it is preferable to use a fibrous material fora core on surfaces of which a binding agent is high in concentration andcured layers are provided. With some binding agents, cured layers may beformed only on surface layers of a molded body and almost a smallquantity of binding agent having permeated inside is moved to thesurface layers due to migration to form little cured layers inside. Inthis case, it is feared that crack is generated inside and an entiremolded body is decreased in strength. In contrast, it is preferable toobtain a plate-shaped molded body by forming fibers into a plate shape,thereafter coating a binding agent on surfaces thereof, and subjectingthe formed fiber to compressing and heating. Thus layers having a highconcentration owing to curing of the coated binding agent are formed onthe surface layers. A small quantity of binding agent permeated insidedoes not migrate so much but is cured inside the surface layers.Consequently, it is possible to obtain a molded body in which thebinding agent is varied in concentration in a through-thicknessdirection and a small quantity of binding agent is cured inside, andwhich is excellent in strength.

Inorganic fibers are desirable in terms of heat resistance at the timeof compressing and heating. Especially, glass wool and glass fiber arepreferable because of a high weather resistance and a favorable waterresistance. In particular, inorganic fibers made of boron containingglass are desirable because of excellent weather resistance and waterresistance.

In case of forming a core from fibers, the fibers are not specificallylimited in fiber diameter. From the viewpoint of enabling forming acontinuous porous structure and obtaining a core which is high surfacehardness and lightweight, the fiber diameter desirably ranges from 0.1to 20 μm, preferably from 1 to 10 μm, and further preferably from 2 to 7μm. In particular, in case of forming a core from a laminate, fibershaving an average fiber length of 5 to 15 mm are preferably used fromthe viewpoint of preventing peel of the laminate but not limitative.Non-woven web may be used in the same manner as in the first exemplaryembodiment.

The powder described above may be added to a fibrous material for acore. Known materials such as pulverized pieces of a foam resin such asurethane foam, phenol foam, styrene foam, etc. may be usedappropriately.

Inorganic or organic binding agents described with respect to the secondto fourth exemplary embodiment are usable as a binding agent.Alternatively, organic binding agents formed of thermoplastic resinssuch as vinyl acetate, acrylic resins, etc., or natural adhesives, etc.will do. It is also possible to mix these materials for use, or todilute them with water or a known organic solvent for use. However, itis preferable to use an inorganic material for a binding agent. Byvirtue of using an inorganic material for a binding agent, gasesgenerated from the binding agent with passage of time decrease and avacuum heat insulator is enhanced in adiabatic performance with passageof time. Further, the binding agent preferably contains at least one ofboric acid, borate, or phosphoric acid, phosphate, or heated productsthereof. Some ones of these substance themselves form a glassy substanceand have a good affinity for glass fibers to be hard to migrate.

A method of adhering a binding agent to a core material is notspecifically prescribed but includes adhering by coating or spraying abinding agent or its diluted solution. Concretely, a binding agent issprayed after a core material is molded to some extent, and thereaftercompressing and heating is performed, thereby enabling obtaining amolded body, in which the binding agent is varied in concentration in athrough-thickness direction of the plate-shaped molded body.

In case of using a fibrous material for a core, a binding agent or itsdiluted solution is sprayed at the time of fiberization. Fibers in whicha binding agent is large in concentration are arranged in certainportions of a plate-shaped molded body, and fibers, in which a bindingagent is small in concentration or a binding agent is absent, arearranged in the remaining portions. Thereafter, a fiber laminated bodyis solidified by compressing and heating or the like. By fabricating acore in this manner, a board, in which a binding agent is varied inconcentration in a through-thickness direction of a molded body, is alsoobtained.

A core varied in concentration in a through-thickness direction is alsoobtained by combining two or more of a plate-shaped molded body, inwhich a binding agent is large in concentration, and a plate-shapedmolded body, in which a binding agent is small in concentration.

It is desirable to make a binding agent adhering in a manner that theagent has a concentration in which a solid of the binding agent is atleast 0.1 wt % but at most 20 wt % relative to the binding agent. Thisis because as a binding agent is increased in quantity, an increase ingases generated from the binding agent and an increase in solid thermalconductivity are feared to have adverse influences on the adiabaticperformance of a vacuum heat insulator. On the other hand, a fiberlaminated body is insufficiently solidified when a binding agent issmall in quantity.

It suffices that a binding agent is different in concentration at leastbetween certain portions and other certain portions in athrough-thickness direction of a core. It aims at producing an effectthat those portions in which a binding agent is small in concentrationare decreased in solid thermal conductivity and resistance toexhaustion, and those portions in which a binding agent is large inconcentration are given stiffness of a board. In particular, thoseportions in which a binding agent is large in concentration preferablydefine at least one surface layer of a core or both surface layers. Thisis because a finished vacuum heat insulator is excellent in strength andfavorable in surface flatness.

As similar to the first to fifth exemplary embodiments, it is desiredthat a core be molded to have a density of 100 kg/m³ to 400 kg/m³, anddensity may be varied inside. A core more preferably has a density offrom 120 to 300 kg/m³ and further preferably from 150 to 250 kg/m³. Thereason for this is the same as in the fifth exemplary embodiment.

Core 2 preferably has a surface hardness of 15 to 70 and desirablypreferably a surface hardness in the range of 20 to 40. With the surfacehardness of 15 or more, it is possible to ensure a handling quality andsurface flatness. On the other hand, with the surface hardness of 70 orless, waste disposal of heat insulators is facilitated afterrefrigerators are discharged. The surface hardness corresponds to thatof core 2 prior to packaging with exterior covering 3. Accordingly, avacuum heat insulator after packaging with exterior covering 3preferably has a surface hardness of 50 to 80 and desirably a surfacehardness in the range of 60 to 75.

The surface hardness manifests owing to formation of a cured layer onsurfaces of core 2, and fibers or powder particles in the cured layerare thermally fixed by a binding agent. That is, fibers or powderparticles are bound by the binding agent to thereby achieve formation ofthe cured layer. The cured layer is small in void ratio and formed bybinding of fibers or powder with the binding agent whereby it is high instiffness. Accordingly, by forming such cured layer at least on onesurface of core 2, preferably on both surfaces thereof, core 2 isenhanced in stiffness and made favorable in handling quality. Since core2 is increased in hardness, depression or large irregularities arelittle generated on the surfaces of heat insulator 1 and flatness on thesurfaces can be maintained even after the core is surrounded by exteriorcovering 3 and an interior of the exterior covering is reduced inpressure and sealed. Therefore, adhesiveness at the time of mounting torefrigerating/cooling equipment is improved and the adiabatic effect ismade further favorable.

The vacuum heat insulator 1 according to the sixth to eighth exemplaryembodiments is lightweight, high in stiffness and planar accuracybecause it contains therein a small quantity of binding agent, so onehaving a large area is usable.

Being varied depending upon type, application quantity, and addition ofthe binding agent, concentration of the water solution of the bindingagent cannot be unconditionally prescribed but is desirably 0.5 to 20 wt% in view of solubility in water. An application quantity of awater-diluted solution of the binding agent is not specificallyprescribed but is preferably at least half but at most 3 times thefibrous material in weight ratio. This is because with less than half,the water solution is hard to permeate inside the laminated fibers, andwith more than 3 times, surplus water content in a liquid state outflowsin the subsequent heating and compressing process, and the binding agentalso outflows along therewith to cause loss in the binding agent.

Ninth Exemplary Embodiment

A vacuum heat insulator according to a ninth exemplary embodiment is thesame in fundamental constitution as that of the sixth exemplaryembodiment. In the vacuum heat insulator according to this embodiment, acured layer is formed by spraying water on surfaces of a core.

A method of manufacturing a core according to this embodiment will bedescribed below.

A raw stock of glass fibers manufactured by the centrifuge method andhaving an average fiber diameter of about 4 μm to 6 μm is cut to apredetermined size and aggregated in a predetermined amount to belaminated. Ion exchanged water around a neutrality of a PH value of atleast 6 but at most 8 is sprayed onto surfaces of a fiber laminate in amanner to adhere evenly thereto. A sprayed quantity is made 1.5 to 2.0times in a weight of the fiber laminate.

The fiber laminate onto which the ion exchanged water is sprayed iscompressed at room temperature around 25° C. to make the water diffusedand permeated inside the fiber laminate. The fiber laminate is subjectedto high-temperature compression in a heating press to be held for 10minutes or longer to be dried, thus fabricating molded body 5 having athickness of 10 mm. In the high-temperature compression, the laminate isplaced in a metallic jig heated to 380° C. and is pressed from above bya metallic presser plate.

The molded body thus obtained is hard to be split in a direction oflamination and made high in reliability because glass fibers areoriented perpendicular to a direction of heat transmission by repeatedcompression.

A molded body fabricated to have a thickness of 10 mm is cut to 180mm×180 mm sized pieces to form core 2. Core 2 is dried in a dryingfurnace at 150° C. for about 60 minutes and water moisture remainingafter molding is removed.

Dried core 2 is taken out from the drying furnace, an adsorbent isquickly received into recesses, which have been beforehand formed incore 2, and core 2 receiving therein the adsorbent is inserted intoexterior covering 3 to be placed in a vacuum chamber. An interior of thevacuum chamber is reduced in pressure and exhausted to have a degree ofvacuum of at most 1.33 Pa, in which state an opening of exteriorcovering 3 is thermally fused in the vacuum chamber to be sealed. Thus avacuum heat insulator 1 is obtained.

A cured layer of core 2 thus structured is formed by simply sprayingwater on the surfaces of the laminate. That is, fibers are bound by thatsubstance which is eluted from the fibers due to adhesion of water. Thesubstance thus eluted from the fibers functions as a binding agent. Withthe method with water spraying, water does not completely permeate aninner layer and the inner layer becomes weak in binding strength, sothat it is possible to obtain a core in which the inner a layer thesofter the layer.

While ion exchanged water is used as water being sprayed onto the fiberlaminate, it is not specifically limitative but distilled water, alkaliion water, mineral water, filtered pure water, or city water will alsobe used.

As characteristic values of water, hardness, total alkalinity,concentration of chlorine residue, concentrations of ions such as basicnitrogen e.g., nitrous acidic, nitric acidic, and ammoniacal nitrogen,phosphoric acid, copper, and iron are not specifically limitative.However, ion exchanged water is preferable in terms of adiabaticperformance.

An adsorbent is received if desired and may not be used especially.

The thermal conductivity of vacuum heat insulator 1 obtained in thismanner is measured at an average temperature 24° C. to be 0.0020 W/mK.In a test for reliability with passage of time corresponding to 10years, a value of thermal conductivity is 0.025 W/mK and sodeterioration is slight.

The density of core 2 is found by measuring weight and volume of vacuumheat insulator 1, unsealing exterior covering 3 of vacuum heat insulator1, and measuring weight and volume of exterior covering 3 and theadsorbent to subtract the same from the values of vacuum heat insulator1.

The density of core 2, according to this embodiment, thus found is 250kg/m³.

Tenth Exemplary Embodiment

FIG. 6 is a cross sectional view of a vacuum heat insulator according toa tenth exemplary embodiment of the present invention. FIG. 7 is a planview of the vacuum heat insulator according to the tenth exemplaryembodiment of the present invention. Being the same in fundamentalconstitution and materials as those of the sixth to eighth exemplaryembodiments, vacuum heat insulator 1 according to this embodiment isformed on a surface thereof with groove 32.

Subsequently, a method of manufacturing vacuum heat insulator 1 will bedescribed.

First, a plate-shaped vacuum heat insulator is fabricated in the samemanner as in the exemplary embodiment. The thermal conductivity of suchvacuum heat insulator is 0.0023 W/mK at an average temperature 24° C.

Thereafter, the vacuum heat insulator is pressingly narrowed in pressmolding with the use of a molding die to be formed on a surface thereofwith groove 32, dimensions of which are 50 mm at an opening, 20 mm at abottom surface (straight portion), and 5 mm in depth. Corner portions ofthe molding die in pressure contact with exterior covering 3 assume acylindrical shape.

Groove 32 thus formed suffers no damage such as pin holes or the like tothe surface of exterior covering 3 and the thermal conductivity is notvaried except groove 32.

In evaluating deterioration of the heat insulator through an acceleratedtest in order to ascertain reliability with passage of time, the thermalconductivity under conditions of passage of 10 years is 0.0055 W/mK atan average temperature 24° C., and there is no difference between thevacuum heat insulator and a vacuum heat insulator formed with no groove.

That is, since a binder in the inner layer of core 2 is small inconcentration and the inner portion is soft, there is caused no problemin forming groove 32 by means of press molding after fabrication of thevacuum heat insulator. Groove 32 can be molded at a relatively smallpressure of pressing in the atmosphere with the use of a commonapparatus. Groove 32 is in some cases necessary to keep out of otherconstituent elements when an adiabatic box, to which vacuum heatinsulator 1 is applied, is to be formed. Groove 32 is readily formed onvacuum heat insulator 1 according to the invention to lead to animprovement in productivity and reduction on cost.

Eleventh Exemplary Embodiment

Vacuum heat insulator 1 according to this embodiment is fabricated inthe same manner as in the sixth to eighth exemplary embodiments after agroove is formed on a core fabricated in the sixth to eighth exemplaryembodiments by means of cutting. In this stage, vacuum heat insulator 1having been formed with groove 32 is resulted.

The thermal conductivity of vacuum heat insulator 1 is the same as thatin the exemplary embodiment and the thermal conductivity underconditions of passage of 10 years also has no difference therebetween.

That is, since a binder in the inner layer of the core is small inconcentration and the inner portion is soft, the groove is readilyformed on the molded body and there is no fear of damage to the exteriorcovering possibly caused by a molding die.

The groove may be formed by that molding die, which is used in heatingand compressing molded body 4.

With respect to the tenth and eleventh exemplary embodiments, anexplanation is given to the vacuum heat insulator making use of a coreon surfaces of which a binding agent is large in quantity and which isformed with a cured layer. However, like the sixth to eighth exemplaryembodiments, it suffices that a soft layer having a small quantity ofbinding agent is present somewhere in a through-thickness direction of acore. An explanation for other materials or the like is the same as inthe sixth to eighth exemplary embodiments.

Twelfth Exemplary Embodiment

A vacuum heat insulator according to a twelfth exemplary embodiment isthe same in fundamental constitution and materials as those of the ninthexemplary embodiment. A groove is formed on a surface of such vacuumheat insulator. While the method is the same as that in the tenthexemplary embodiment, a molded body obtained in case of using water issofter than that in case of using a binder, and damage to a exteriorcovering is small.

Thirteenth Exemplary Embodiment

A vacuum heat insulator according to a thirteenth exemplary embodimentis the same in fundamental cross sectional structure as that of thefirst exemplary embodiment shown in FIG. 1. Core 2 is different inconstitution from that in the first exemplary embodiment.

Core 2 is a plate-shaped molded body composed of a glass wool boardformed by hot pressure forming in a dry process by means of a bindingagent. Core 2 contains fibers having short fiber lengths. Table 2indicates results of structuring vacuum heat insulator 1 by the use ofcore samples A to D having different fiber lengths and different ratiosof content of fibers and evaluating them in terms of thermalconductivity. Compressibility indicated in Table 2 is found from aration of that thickness of care 2 after structuring of a vacuum heatinsulator which is found from a thickness of vacuum heat insulator 1,and a thickness of core 2 prior to structuring of the vacuum heatinsulator.

FIG. 8 shows a state in which vacuum heat insulator 1 making use of thesample C is unsealed and core 2 is taken out for observation. In thestate shown in FIG. 8, an optical microscope is used under the conditionof standard temperature and pressure to make observation in photographicmagnification of 200 (objective lens magnification; ×50). As shown inthe figure, fibers are oriented perpendicular to a direction of heattransmission. Table 2 indicates results of measuring fiber lengths oftotal fibers present in a range of observation and counting the numberof fibers assuming that fibers beyond the range have a fiber length ofat least 100 μm.

TABLE 2 A B C D Thermal conductivity 0.0025 0.0025 0.0025 0.0050 (W/mK)Density (kg/m³) 300 270 500 250 Compressibility (%) 15 10 40 Fiber 10 μmor 6 2 4 0 length smaller to 20 μm 11 3 8 2 to 30 μm 11 5 7 2 to 40 μm 84 7 6 to 50 μm 1 3 2 1 to 60 μm 3 5 6 5 to 70 μm 1 1 2 2 to 80 μm 3 1 34 to 90 μm 1 2 3 0 to 100 μm 0 4 2 1 Larger than 67 28 19 68 100 μmNumber of fibers of 45 30 44 33 100 μm or smaller Number of fibers of 6728 19 68 larger than 100 μm Ratio (%) of fibers of 40 52 70 25 100 μm orsmaller

Table 2 also indicates results of adjusting data and calculating thenumber of fibers having a fiber length of 100 μm or smaller.

As apparent from Table 2, heat transmission by fibers is interrupted byinclusion of short fibers, when fibers having a fiber length of 100 μmor smaller are included in the range of 40% or more. Therefore, vacuumheat insulator 1 possesses a low initial thermal conductivity. That is,the vacuum heat insulator is excellent in adiabatic performance. In thecase where fibers having a fiber length of 100 μm or smaller areincluded in the range of less than 40% as in the sample D, heattransmission through fibers is much so the vacuum heat insulator providea high thermal conductivity.

In the case where the content of fibers having a fiber length of 100 μmor smaller exceeds 70%, short fibers oriented in a direction of heattransmission increase to cause an increase in solid heat transmission,thus lowering the adiabatic performance.

As described in the first exemplary embodiment, a getter substance suchas a gas adsorbent, a moisture adsorbent, etc. may be incorporated intovacuum heat insulator 1.

While various organic and inorganic materials described in the first tofifth exemplary embodiments are applicable to fibrous materials and abonding agent used for core 2, inorganic materials are desirable for theboth materials from the viewpoint of reliability over a long term.

Fourteenth Exemplary Embodiment

FIG. 9 is a cross sectional view of an adiabatic element according to afourteenth exemplary embodiment of the present invention. Adiabaticelement 8 according to this embodiment includes vacuum heat insulator 1according to any one of the first to ninth exemplary embodiments.Alternatively, the vacuum heat insulator according to the thirteenthexemplary embodiment may be used. Vacuum heat insulator 1 is arranged ina space enclosed by plate elements 9A, 9B as an exterior covering andframe 9C connecting outer peripheries of plate elements 9A, 9B togetherin such a manner that one flat surface of vacuum heat insulator 1contacts closely with plate element 9A. Foamy heat insulator 10 as aheat insulator other than the vacuum heat insulator is filled in a spaceexcept vacuum heat insulator 1. Vacuum heat insulator 1 and adiabaticelement 8 are in the form of a plate. Foamy heat insulator 10 is, forexample, rigid urethane foam. It may be phenol foam, styrene foam, etc.

Plate elements 9A, 9B and frame 9C are made of metals and rigid resins,and all of them may be made of the same material, or one of plateelements 9A, 9B may be made of metal and the other may be made of aresin. Frame 9C may be formed integral with plate element 9A or plateelement 9B.

According to this embodiment, only one flat surface of vacuum heatinsulator 1 is made in close contact with plate element 9A but the otherflat surface of vacuum heat insulator 1 may also be made in closecontact with plate element 9B. Desirably, that surface of plate element9A or 9B, which is made in close contact with the flat surface of vacuumheat insulator 1, is high in flatness.

In place of foamy heat insulator 10, polystyrene foam may be used as aheat insulator other than the vacuum heat insulator.

According to this embodiment, plate elements 9A, 9B, frame 9C, and foamyheat insulator 10 protect vacuum heat insulator 1 from damage caused byexternal forces and maintain a low pressure state inside vacuum heatinsulator 1. Therefore, the adiabatic performance of vacuum heatinsulator 1 is maintained over a long term, and hence the adiabaticperformance of adiabatic element 8 is maintained over a long term. Sincefillet-shaped fused portions 3A of exterior covering 3 of vacuum heatinsulator 1 are hidden, protected, and fixed, handling becomes easy toenlarge a range in which vacuum heat insulator 1 is applied. Sincevacuum heat insulator 1 has a high adiabatic performance and the corehas a great mechanical strength, it is possible to decrease a thicknessof vacuum heat insulator 1 and hence a thickness of adiabatic element 8.

According to this embodiment, foamy heat insulator 10 is filled in thatportion of the space enclosed by plate elements 9A, 9B and frame 9Cserving as an exterior covering, which is not occupied by vacuum heatinsulator 1. Thereby, it is easy to fill a space between the exteriorcoverings and vacuum heat insulator 1 with foamy heat insulator 10 owingto flowability thereof at the time of filling. Thin vacuum heatinsulator 1 is usable also in case of arranging foamy heat insulator 10between one surface of vacuum heat insulator 1 and the exteriorcovering. Therefore, a gap for filling of foamy heat insulator 10 isensured between one surface of vacuum heat insulator 1 and plate element9A to such an extent that flowability (filling quality) of foamy heatinsulator 10 is not hindered, whereby adiabatic element 8 having anexcellent adiabatic property is provided.

A foaming agent used in foaming foamy heat insulator 10 such as rigidurethane foam is not specifically limitative. From the viewpoint ofprotection of the ozone layer and prevention of global warming, thefoaming agent desirably includes cyclopentane, isopentane, n-pentane,isobutane, n-butane, water (foaming of carbon dioxide), azo compounds,argon, etc. In particular, cyclopentane is desirable in terms ofadiabatic performance.

Fifteenth Exemplary Embodiment

FIG. 10 is a cross sectional view of a storage shed according to afifteenth exemplary embodiment of the present invention.

The storage shed according to this embodiment has outer box 11,partition plate 12, inner box 13, and adiabatic element 8. Outer box 11defines an outer shell of the storage shed itself. Partition plate 12compartments an interior of outer box 11 into an upper storage room anda lower machine room. Inner box 13 is arranged apart from inner surfacesof outer box 11 and an upper surface of partition plate 12 withpredetermined spaces, and inner box 13 defines inner wall surfaces ofthe storage room. All outer box 11, partition plate 12, and inner box 13are made of metal or a rigid resin. Adiabatic elements 8A, 8B arearranged as heat insulating plates between outer box 11 and inner box 13and between partition plate 12 and inner box 13. Adiabatic element 8Cserves as an adiabatic partition to compartment the storage room intotwo rooms of different temperatures. Adiabatic elements 8A to 8C are thesame in structure as adiabatic element 8 in the fourteenth exemplaryembodiment.

Since exterior coverings of adiabatic elements 8A, 8B are protected byouter box 11, partition plate 12, and inner box 13, they may berelatively weak in mechanical strength. On the other hand, an exteriorcovering of adiabatic element 8C is preferably made of a metal having arelatively high mechanical strength so as to eliminate the need ofproviding a protective member for surface protection.

With the storage shed according to this embodiment, adiabatic elements 8according to the fourteenth embodiment are combined to form adiabaticwalls for heat insulation of an interior of the storage shed. Thereby,there is provided a storage shed, in which the adiabatic walls are highin mechanical strength and excellent in adiabatic property.Alternatively, the adiabatic walls are decreased in thickness to providea storage shed increased in inner volume or decreased in outsidedimensions.

With the storage shed according to this embodiment, adiabatic elements 8according to the fourteenth exemplary embodiment serve as an adiabaticpartition plate to compartment the interior of the storage shed into aplurality of rooms at different temperatures. Thereby, a quantity ofheat transmitted between the rooms compartmented by adiabatic element 8Cis decreased. Alternatively, adiabatic element 8C is decreased inthickness to increase inner volumes of the storage rooms. Alternatively,the storage shed is decreased in outside dimensions.

The storage shed according to this embodiment is applicable to automaticvending machines and cold showcases. While adiabatic element 8C shown inFIG. 10 divides the storage room laterally into two sections, thestorage room may be divided into two or more sections, or dividedvertically.

Sixteenth Exemplary Embodiment

FIG. 11 is a cross sectional view of an adiabatic box, adiabatic doors,a storage shed, and a refrigerator composed of them, according to asixteenth exemplary embodiment of the present invention.

Adiabatic box 14 according to this embodiment has vacuum heat insulator1 according to any one of the first to ninth and thirteenth exemplaryembodiments. Vacuum heat insulators 1 are arranged in a space surroundedby outer box 15 and inner box 16 as exterior coverings. Each one ofsurfaces of vacuum heat insulators 1 is arranged in a manner to contactclosely with outer box 15 or inner box 16 which defines a bottom surfaceof adiabatic partition wall 14A. Outer box 15 and inner box 16 are madeof metal or synthetic resins. Vacuum heat insulators 1 are plate-shaped.Foamy heat insulator 17 other than the vacuum heat insulator is filledin a space except vacuum heat insulators 1. As similar to foamy heatinsulator 10 according to the fourteenth exemplary embodiment, foamyheat insulator 17 is made of, for example, rigid urethane foam. Thusadiabatic box 14 is of dual-layered structure to include vacuum heatinsulators 1 and foamy heat insulator 17, and in the form of a box.

In manufacture of adiabatic box 14, vacuum heat insulators 1 arebeforehand bonded and fixed to outer box 15, and inner box 16 whichdefines the bottom surface of adiabatic partition wall 14A, and a rawmaterial of foamy heat insulator 17 is injected to be foamed integrally.

Vacuum heat insulators 1 are arranged substantially evenly on respectivesurfaces, that is, both side surfaces, a roof surface, a back surface,and a bottom surface of adiabatic box 14 to occupy 80% of a surface areaof outer box 15.

With adiabatic box 14 according to this embodiment, outer box 15, innerbox 16, and foamy heat insulator 10 protect vacuum heat insulators 1from damage due to external forces. Accordingly, a low pressure stateinside vacuum heat insulators 1 is kept, so that the adiabaticperformance of vacuum heat insulators 1 is maintained over a long term.Therefore, the adiabatic performance of adiabatic box 14 is maintainedover a long term. Since vacuum heat insulators 1 are high in adiabaticperformance and cores thereof are high in mechanical strength, vacuumheat insulators 1 can be made small in thickness and hence wallsdefining adiabatic box 14 become small in thickness.

With adiabatic box 14 according to this embodiment, foamy heat insulator17 is filled in the space except vacuum heat insulators 1. Therefore, itis easy to fill a space between exterior coverings and vacuum heatinsulators 1 with foamy heat insulator 17 owing to flowability thereofat the time of filling. Thin vacuum heat insulator 1 is usable also incase of arranging foamy heat insulator 17 between one surface of vacuumheat insulator 1 and the exterior covering. Therefore, a gap for fillingof foamy heat insulator 17 can be ensured between one surface of vacuumheat insulator 1 and outer box 15, or inner box 16 which defines thebottom surface of adiabatic partition wall 14A, to such an extent thatflowability (filling quality) of foamy heat insulator 17 is nothindered. Thus adiabatic box 14 having an excellent adiabatic propertyis provided.

When adiabatic box 14 is structured to have the same thickness as thatin the conventional one, adiabatic box 14 is superior in adiabaticproperty to that in the conventional one and, in the case whereadiabatic box 14 is made the same in adiabatic property as that in theconventional one, walls defining adiabatic box 14 are decreased inthickness as compared with that in the conventional one.

Adiabatic box 14 according to this embodiment is structured integralwith adiabatic partition wall 14A. However, adiabatic partition wall 14Amay be made separately in the form of a plate like the adiabatic elementaccording to the fourteenth exemplary embodiment and incorporated intoadiabatic box 14.

Each of adiabatic doors 18 according to this embodiment has vacuum heatinsulator 1 according to any one of the first to ninth and thirteenthexemplary embodiments. Vacuum heat insulator 1 is arranged in a spacesurrounded by outside surface plate 19 and inside surface plate 20 asexterior coverings. Outside surface plate 19 and inside surface plate 20are made of metal or synthetic resins. One surface of vacuum heatinsulator 1 is arranged in a manner to contact closely with outsidesurface plate 19. Foamy heat insulator 17 other than the vacuum heatinsulator is filled in a space except vacuum heat insulator 1. Each ofadiabatic door 18 is of dual-layered structure composed of vacuum heatinsulator 1 and foamy heat insulator 17, and plate-shaped to close afront opening of adiabatic box 14 in an openable and closable manner.

In manufacture of adiabatic door 18, vacuum heat insulator 1 isbeforehand bonded and fixed to the outside surface plate 19, and a rawmaterial of foamy heat insulator 17 is injected to be foamed integrally.

With adiabatic door 18 according to this embodiment, outside surfaceplate 19, inside surface plate 20, and foamy heat insulator 17 protectvacuum heat insulator 1 from damage due to external forces. Foamy heatinsulator 17 is filled in a space except vacuum heat insulator 1. Thusin the same manner as with the adiabatic box described above, a thinvacuum heat insulator having an excellent adiabatic property, which ismaintained over a long term, is obtained and adiabatic doors 18 havingthe same properties are provided.

The storage shed according to this embodiment includes adiabatic box 14,adiabatic doors 18, and the storage rooms formed in a space surroundedby adiabatic box 14 and adiabatic doors 18. Vacuum heat insulators 1 areused for both adiabatic box 14 and adiabatic doors 18 to enhance theadiabatic property of adiabatic box 14 and adiabatic doors 18. With suchconstruction, the storage room is increased in inner volume by makingadiabatic box 14 and adiabatic door 18 small in thickness.Alternatively, the storage room is decreased in outside dimensions.

The refrigerator according to this embodiment has adiabatic box 14,adiabatic doors 18, the storage rooms, and a cooling device. The storagerooms are formed in a space surrounded by adiabatic box 14 and adiabaticdoors 18 to include freezing room 21 at −15° C. to −25° C. in a lowerstage, cold storage room 22 at 0° C. to 10° C. in an upper stage, andvegetable room 23 at 0° C. to 10° C. in a middle stage. The coolingdevice cools freezing room 21, cold storage room 22, and vegetable room23. The cooling device includes compressor 24, condenser 25, freezingroom cooler (referred below to as cooler) 26, and cold storage roomcooler (referred below to as cooler) 27. Compressor 24 is arranged on aback surface side of a machine room formed at a bottom of adiabatic box14. Condenser 25 is positioned below freezing room 21 within the machineroom. Cooler 26 is arranged on a back surface of freezing room 21.Cooler 27 is arranged on a back surface of cold storage room 22.Adiabatic partition wall 14A is arranged between freezing room 21 andcold storage room 22, which are different in storage temperature fromeach other. Adiabatic partition wall 14A may be provided with a notch(not shown), in which a damper (not shown) is mounted so that cooler 26acts to cool cold storage room 22 and vegetable room 23 without theprovision of cooler 27.

Refrigerant used in the cooling device may be Freon 134a, isobutane,n-butane, propane, ammonia, carbon dioxide, and water, and is notspecifically limitative.

The refrigerator according to this embodiment has vacuum heat insulator1 described in the first to ninth and thirteenth exemplary embodiments.The refrigerator thus constructed is made highly adiabatic because of asharply excellent adiabatic performance relative to that of conventionalfoamy heat insulators. Accordingly, compressor 24 serving to cool aninterior of the storage shed countering invasion of heat from outside issharply reduced in operation time. That is, the cooling device servingto cool the cold storage rooms (freezing room 21, cold storage room 22,and vegetable room 23) to predetermined temperatures is reduced inoperational energy to contribute to energy saving. Alternatively, withthe refrigerator thus constructed, the cold storage room can beincreased in inner volume or reduced in outside dimensions.

Adiabatic box 14 and adiabatic doors 18 according to this embodiment areof dual-layered structure composed of vacuum heat insulators 1 and foamyheat insulator 17. Thereby, in addition to the effect of vacuum heatinsulator 1 according to any one of the first to ninth and thirteenthexemplary embodiments, the vacuum heat insulators are combined withfoamy heat insulator 17 in adiabatic box 14 to thereby achieve anincrease of the box in strength. Therefore, even when vacuum heatinsulators 1 are positioned between outer box 15 and inner box 16 andbetween outside surface plate 19 and inside surface plate 20, betweenwhich foamy heat insulator 17 is filled, distortion and indentation arenot generated on outer box 15, inner box 16, and outside surface plate19. Accordingly, the adiabatic box and the adiabatic door are providedto be excellent in adiabatic performance.

Seventeenth Exemplary Embodiment

A cross sectional view of a refrigerator according to a seventeenthexemplary embodiment of the present invention is the same as FIG. 11showing the sixteenth exemplary embodiment.

According to this embodiment, vacuum heat insulator 1 described in thesixth to eighth exemplary embodiments is used. Vacuum heat insulator 1is arranged on outer box 15 inside the box such that a surface thereofon that side, on which a cured layer of core 2 is formed, faces an innersurface of outer box 15.

An amount of electric power consumption of the refrigerator thusconstructed is decreased 25% relative to that of a refrigerator providedwith no vacuum heat insulator.

A freezing equipment, and a cooling equipment, that is, a refrigerator,which is excellent in adiabatic performance, is obtained by arrangingthe vacuum heat insulators, which is excellent in adiabatic performance,according to the sixth to eighth exemplary embodiments, in a spacedefined by the outer box and the inner box and filling foamy heatinsulator in a space except the vacuum heat insulators. Since the curedlayer is formed on the surface of core 2, stiffness of the core is high.Thereby, a refrigerator of energy saving and excellent outwardappearance is obtained, in which the outward appearance (planaraccuracy) of outer box 15 and the adiabatic performance of the adiabaticbox can be made higher-dimensionally compatible.

Eighteenth Exemplary Embodiment

A cross sectional view of a refrigerator according to an eighteenthexemplary embodiment of the present invention is the same as FIG. 11 inthe sixteenth exemplary embodiment. According to this embodiment, thevacuum heat insulator described in the tenth to twelfth exemplaryembodiments is used.

FIG. 12 is an enlarged, cross sectional view of an essential part of aroof surface of a refrigerator according to this embodiment.

Preferably, vacuum heat insulator 1 formed with groove 32 capable ofreceiving therein refrigerant pipe 31 is arranged on that portion of aninner surface of outer box 15, where refrigerant pipe 31 is arranged,such that refrigerant pipe 31 is received in the groove 32. Vacuum heatinsulator 1 thus formed with groove 32 is described with respect to thetenth to twelfth exemplary embodiments. Generally, a plurality of smallvacuum heat insulators are arranged on that portion of the inner surfaceof outer box 15, on which refrigerant pipe 31 is arranged, keeping awayfrom the refrigerant pipe 31. On the other hand, according to thisembodiment, large vacuum heat insulator 1 can be arranged in a manner tocover refrigerant pipe 31. Therefore, a refrigerator excellent in energysaving can be obtained, in which a small number of vacuum heatinsulators 1 makes it possible to efficiently prevent heat of outer box15 and the refrigerant pipe 31 from being transmitted to an interior ofthe refrigerator.

Vacuum heat insulator 1 is fixed to outer box 15 by means ofthermoplastic, gelled, hot melt adhesive (referred below to as adhesive)33. A layer of adhesive 33 has a thickness of about 100 μm. Thethickness preferably ranges from 70 to 130 μm. Adhesive 33 is coatedevenly on a surface of vacuum heat insulator 1 in proper quantities bymeans of a roller or the like. The surface is to be bonded to outer box15. The provision of a layer of adhesive 33 having a thickness over 130μm leads to waste of the adhesive and reduction in adiabatic performancebecause adhesive 33 transmits heat more easily than the foamy heatinsulator. When the layer of adhesive 33 is less than 70 μm inthickness, reliability in adhesion is lowered. While a two-sided tapecan be used in place of adhesive 33 for fixation, a hot melt adhesive ispreferable in terms of reliability in adhesion. A type of hot meltadhesive is not specifically limitative and there are listed ones, ofwhich a base includes ethylene-vinyl acetate copolymer resin, polyamideresin, polyester resin, synthetic rubber, etc.

Adhesive 33 may be used for fixation of vacuum heat insulator 1 in thesixteenth and seventeenth exemplary embodiments.

According to this embodiment, refrigerant pipe 31 is received in groove32. In the case where a portion, on which vacuum heat insulator 1 isarranged, is not planar, however, groove 32 may be provided in a mannerto receive projections.

While an effect is produced when the vacuum heat insulator is applied toa location in the refrigerator according to the sixteenth to eighteenthexemplary embodiments, where is large in temperature difference betweenoutside and inside the refrigerator, the coverage of 50% or morerelative to a surface area of the outer box is desirable. When thecoverage is over 50%, influences due to heat loss in rigid urethane foamare decreased and insulation effectiveness owing to application of thevacuum heat insulator becomes dominant, so that efficient heatinsulation becomes possible.

It is preferable to use inorganic fibers for a core of the vacuum heatinsulator. Since inorganic fibers are nonflammable, the refrigerator isenhanced in safety.

The refrigerator according to this embodiments is shown as a typicalexample of equipments, which operate in the temperature zone of −30° C.to room temperature, at which heat insulation is required. This vacuumheat insulator is also usable in, for example, insulated vans,refrigerators making use of thermoelectric refrigeration, etc. Coldequipments, such as automatic vending machines, making use of cold andwarmth in a range up to high temperatures come within the category ofthe present invention. Gas equipments, or equipments such as coolerboxes, etc., requiring no power are also included.

Further, the vacuum heat insulator is also usable in personal computers,jar pots, rice cookers, etc.

INDUSTRIAL APPLICABILITY

The vacuum heat insulator according to the present invention includes acore molded to be plate-shaped with the use of a binding agent. Thevacuum heat insulator assumes any one of the following configurations.

A) The core is formed by curing a fiber aggregate by means of a bindingagent. The fibers have an average fiber diameter of at least 0.1 μm butat most 10 μm, and voids defined by fibers have a void diameter of atmost 40 μm. The core has a percentage of the voids of at least 80%.

B) A binding agent is varied in concentration in a through-thicknessdirection of the core.

C) A cured layer solidified by the binding agent is formed on at leastone side surface of the core.

D) The core contains fibers having a length of at most 100 μm. Thefibers are oriented perpendicular to a direction of heat transmission.

Such vacuum heat insulator is excellent in adiabatic performance.Adiabatic elements, adiabatic doors, adiabatic boxes, storage sheds, andrefrigerators, in which such vacuum heat insulator and a foamy heatinsulator are used, have an excellent adiabatic property, and maintainthe adiabatic property over a long term, so that they can be made thinand small in size. Alternatively, it is possible to increase an innervolume. The refrigerators are excellent in adiabatic property tocontribute to energy saving.

LIST OF REFERENCE NUMERALS IN THE DRAWINGS

-   1: vacuum heat insulator-   2: core-   2A: skin layers-   2B: intermediate layers-   2C: central layer-   3: exterior covering-   4, 4A, 4B: molded body-   5: binding agent-   6: fiber-   8, 8A, 8B, 8C: adiabatic element-   9A, 9B: plate element-   9C: frame-   10, 17: foamy heat insulator-   11, 15: outer box-   12: partition plate-   13, 16: inner box-   14: adiabatic box-   14A: adiabatic partition wall-   18: adiabatic door-   19: outside surface plate-   20: inside surface plate-   21: freezing room-   22: cold storage room-   23: vegetable room-   24: compressor-   25: condenser-   26: freezing-room cooler-   27: cold storage room cooler-   31: refrigerant pipe-   32: groove-   33: adhesive

1. A vacuum heat insulator comprising: a molded plate-shaped core havingan aggregate comprising fibers and a binding agent for curing the fiberaggregate, and an exterior cover enclosing the core in a chamber definedby the exterior cover, the chamber having a pressure lower than apressure outside the chamber, wherein the fibers have an average fiberdiameter between 0.1 μm and 10 μm, voids defined by the fibers have avoid diameter of at most 40 μm, the core comprises at least 90% saidvoids defined by the fibers, and a difference in thickness of the corebetween when the core is subjected to the pressure outside the chamberand when the core is subjected to the pressure inside the chamber is atmost 10%.
 2. A vacuum heat insulator, comprising: a core comprising aplate-shaped molded body containing fibers and a binding agent, theconcentration of the binding agent being larger at a surface of the corethan inside the core in a through-thickness direction thereof, therebydecreasing a solid thermal conductivity of the core, decreasingresistance to exhaustion, and ensuring a strength of the vacuum heatinsulator; and an exterior cover enclosing the core in a chamber definedby the exterior cover, an interior of the chamber having a lowerpressure than an exterior of the chamber, the exterior cover having agroove that extrudes toward a center of the core.
 3. The vacuum heatinsulator according to claim 1, wherein the binding agent contains atleast an organic binder.
 4. The vacuum heat insulator according to claim1, wherein the binding agent contains at least an inorganic binder. 5.The vacuum heat insulator according to claim 1, wherein the bindingagent contains at least a thermosetting binder.
 6. The vacuum heatinsulator according to claim 1, wherein the binding agent contains atleast one of boric acid, borate, phosphoric acid, phosphate, and aheated product thereof.
 7. The vacuum heat insulator according to claim1, wherein the core has a density of between at least 100 kg/m³ and notmore than 400 kg/m³.
 8. The vacuum heat insulator according to claim 1,wherein the fibers are made of an inorganic material.
 9. The vacuum heatinsulator according to claim 1, wherein the fibers contain at least oneof glass wool and glass fibers.
 10. The vacuum heat insulator accordingto claim 1, wherein the fibers constitute a nonwoven web.
 11. The vacuumheat insulator according to claim 1, wherein the core includes alaminate.
 12. The vacuum heat insulator according to claim 1, having athermal conductivity of between at least 0.0015 W/mK and not more than0.0025 W/mK.
 13. A method of manufacturing a vacuum heat insulatoraccording to claim 1, the method comprising steps of: A) covering thecore with the exterior cover, B) reducing the pressure within thechamber so that the core is decreased in thickness by, at most, 10%, andC) sealing an opening of the exterior cover.
 14. The method ofmanufacturing a vacuum heat insulator, according to claim 13, whereinthe fibers are made of an inorganic material.
 15. A heat insulatingelement comprising: the vacuum heat insulator according to claim 1, asecond heat insulator other than the vacuum heat insulator, and a secondexterior cover, wherein the vacuum heat insulator and the second heatinsulator are located within the second exterior cover, and the secondheat insulator occupies space within the second exterior cover that isnot occupied by the vacuum heat insulator.
 16. The heat insulatingelement according to claim 15, wherein the second heat insulator is afoamy heat insulator.
 17. An adiabatic box, wherein the heat insulatingelement according to claim 15 is formed to be box-shaped.
 18. Anadiabatic door comprising the heat insulating element according to claim15.
 19. A storage shed comprising: the adiabatic box according to claim17, and an adiabatic door to cover an opening of the adiabatic box. 20.A storage shed comprising: the heat insulating element according toclaim 15, and an adiabatic wall for thermal insulation of an interior ofthe storage shed.
 21. A storage shed having an adiabatic partition plateincluding the heat insulating element according to claim 15, wherein aninterior of the storage shed is compartmented into a plurality of rooms.22. A refrigerator comprising: the storage shed according to claim 19,and a cooling device to cool a storage room in the storage shed.
 23. Theadiabatic box according to claim 17, wherein the core of the vacuum heatinsulator has a cured layer on at least one side surface thereof, saidcured layer being solidified by a binding agent; and a surface of thevacuum heat insulator on a side of the cured layer faces an innersurface of the second exterior cover.
 24. The refrigerator according toclaim 22, wherein the binding agent has a higher concentration on asurface of the core than inside the core in a through-thicknessdirection thereof, and said exterior cover has a groove extending froman outer surface of the exterior cover toward a center of the core, saidgroove for receiving a projection on a surface on which the vacuum heatinsulator is located.
 25. The refrigerator according to claim 24,wherein the cooling device includes a refrigerant pipe and theprojection is the refrigerant pipe.
 26. The refrigerator according toclaim 22, further comprising an adhesive to fix the vacuum heatinsulator to the second exterior cover.
 27. The refrigerator accordingto claim 26, wherein the adhesive is a hot-melt adhesive.
 28. Therefrigerator according to claim 26, wherein the adhesive has a thicknessof between at least 70 μm and not more than 130 μm.
 29. A method ofmanufacturing a refrigerator, the method comprising: a) manufacturing avacuum heat insulator by the method according to claim 13, b) enclosingthe vacuum heat insulator and a second heat insulator that is not thevacuum heat insulator within a second exterior cover to form a heatinsulating element, c) forming a storage shed from at least one ofadiabatic boxes, adiabatic doors, and adiabatic walls by using the heatinsulating element, and d) mounting a cooling device that cools aninterior of the storage shed.
 30. A refrigerator comprising: the storageshed according to claim 20, and a cooling device to cool a storage roomin the storage shed.
 31. A refrigerator comprising: the storage shedaccording to claim 21, and a cooling device to cool a storage room inthe storage shed.
 32. The refrigerator according to claim 22, whereinthe core of the vacuum heat insulator has a cured layer on at least oneside surface thereof, said cured layer being solidified by a bindingagent; and said exterior cover comprises a groove extending from anexterior surface of the exterior cover toward a center of the core.